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There are two kinds of judgement to goodness of the solvent in polymer solutions. One is Kai= 1/2, from the free energy of Flory-Huggins mean-f ield calculation and the second Virial coefficient in the expansion of the osmotic pressure for dilution solution; another is Kai= 0, from the mixing heat. The former occurs in the current textbooks about polymer physics in China, but the author prefers the latter and gives his reasons.